I remember reading a quote from Apple concerning the hooplah over a low-end ________ computer (fill in the blank however you like: headless iMac, bare-bones, etc.) and it said that Apple chooses not to enter or compete in the low-end, sub-$800 category simply because they don't see a way that they can make money doing that.
While we all wish and hope that Apple exists solely to serve our computing needs, and sometimes we think we know better than Apple, I have to agree with them. eMachines was the "next great thing" in their day -- cheap, throw away computers that cost little to manufacture and even less to sell... now look at them. I want Apple to keep innovating and producing high-quality, mid-to-high-end computers. While a bare-bones customizable Macintosh at under $800 would be awesome, I agree that I don't see the money-making potential in it, and, if it would ultimately hurt Apple in the long run, I say don't do it. At least not until it's feasible.
I'll try and dig up a link for that quote -- I know heresay is no good without some info to back it up.